The shape of the normal eye is maintained by an internal fluid pressure of about 15 mm of mercury. That intraocular pressure (IOP) is controlled by the balance of flow of aqueous humor due to secretion from the ciliary body and drainage through the trabecular meshwork. In diseases of the eye, such as glaucoma, the balance is disturbed.
Typical retinal topography systems are bulky, complex and expensive systems. For example, U.S. Pat. No. 4,423,931 is entitled “Fundus Camera Accessory for Analysis of the Ocular Fundus Contour,” discloses a method of illuminating the off-axis portion of the fundus with a pattern of linear stripes. Since the pattern is incident on the fundus at an angle relative to the fundus perpendicular, any bumps or depressions in the retinal surface will result in curved stripes. When these stripes are viewed through a fundus camera and analyzed, information can be derived about the topography of the retina. Unfortunately, this device requires a bulky off-axis illumination system that is attached to the fundus camera by means of a bracket. This adds to cost, weight, volume, and complexity of the system.
Changes in blood circulation and in the transport of cell components within the nerve fibers have been found in the optic disc during elevation of IOP. Optic nerve head tissue gradually dies, and a “caving in” or excavation of the optic disc deepens and gets wider as glaucoma damages the nerves. These changes in the topography of the optic disc surface are believed to precede visual field loss in many cases. In addition, the topographic changes can be measured objectively, whereas the other tests, such as visual field examination, are highly subjective. A change in optic disc topography is objective evidence that the prevailing IOP is too high for that eye.
Proposed use is for special value fundus lenses that can be use in conjunction with a standard ophthalmoscope or fundus camera for eye examinations or vitreoretinal surgeries.